This invention relates to an internal combustion engine and more particularly to a variable valve timing mechanism for an engine.
In order to improve the performance of internal combustion engines, not only in terms of power output but also in terms of fuel economy and exhaust emission control, it has been proposed to employ variable valve timing mechanisms. These mechanisms permit adjustment of the timing of opening and closing of the intake and/or exhaust valves during the running of the engines. This permits the valve timing to be set optimum for a wide variety of running conditions.
One popular type of variable valve timing mechanism is interposed in the arrangement that couples the engine output shaft to the camshaft. A hydraulically actuated mechanism is interposed in the drive so as to vary the phase relationship between the camshaft and the element which drives it.
Obviously, it is necessary to supply hydraulic fluid to this variable valve timing mechanism for its operation. This involves not only the supply of pressurized fluid but also a return path for returning the fluid from the variable valve timing mechanism during the adjusting cycle.
Frequently, these hydraulic connections are done either externally or in a cover plate of the engine. This gives rise to a number of difficulties. First, the connections may be positioned in an area where they can be damaged. Secondly, there are additional couplings and thus the likelihood of leakage.
It is, therefore, a principal object of this invention to provide an improved hydraulic operating mechanism and supply system for a variable valve timing mechanism of an internal combustion engine.
It is a further object of this invention to provide an improved arrangement for transmitting and discharging actuating hydraulic fluid to the variable valve timing mechanism of an internal combustion engine.
Frequently, the hydraulic fluid for operating the variable valve timing mechanism is the same lubricant that is also employed to lubricate the engine. Thus, in addition to supplying the hydraulic fluid to the variable valve timing mechanism for its actuation, it is also necessary to supply the same fluid to the bearings of the camshaft for their lubrication as well as for the lubrication of other components associated with the camshaft and engine. This further complicates the overall structure.
It is, therefore, an additional object of this invention to provide an improved and simplified hydraulic supply arrangement for supplying lubricating oil to a camshaft for its lubrication and also for the actuation of the variable valve timing mechanism associated with it.